The invention relates to a self-dumping centrifugal separator having a piston valve defining one end of the separating chamber and solids chamber for the control of the ejection openings in the drum periphery, which permits the performance of partial and complete dumping selectively and independently of time, divides the closing chamber into a plurality of successive divisions, and is fed with control fluid in a known manner, hydraulically operated valves being installed in the passages for the discharge of the control fluid.
A centrifugal separator of this kind of construction is known, for example, from German Pat. No. 20 48 429, and is provided with a closing chamber consisting of two divisions, which is placed between the piston valve and the adjacent drum portion and is filled with a control fluid before the beginning of the centrifuging operation. The closing chamber has a greater radius than the interior of the drum, so that, when the chamber is completely filled, the closing pressure acting from this closing chamber side on the piston valve is always greater than the pressure of the drum charge acting from the other side in the opening sense. For the purpose of the ejection of solids, with the drum operating at full speed, control liquid is let out of the divisions of the closing chamber through hydraulically controlled valves, and thus the closing pressure is reduced. Under the pressure of the drum charge, the piston valve then moves to the open position releasing the ejection openings.
Depending on the nature and consistency of the solids being separated, it can be advantageous to perform partial dumping at shorter time intervals, or complete dumping at longer time intervals.
In the performance of partial dumping, the drum is opened only slightly and for a brief period of time, by letting control fluid out of either the inner or the outer division of the closing chamber through valves, so that only a portion of the solids that have collected in the solids chamber is ejected, while the other portion remains in the drum as a safety ring. This prevents the ejection and loss of any large amount of product liquid together with the solids.
Since in a partial dumping, only one division of the closing chamber is emptied of control fluid, the opening duration and the opening width of the self-dumping drum is limited, since control fluid always remains in the other division of the closing chamber. After the ejection of the solids has begun, as soon as the liquid level in the separating chamber has receded to the extent that the opening pressure is lower than the closing pressure of the control fluid remaining in the closing chamber, the piston immediately moves back to the closed position. The greater the closing pressure of the control fluid retained in the closing chamber is, the more rapidly the drum recloses, and the lesser will be the amount of solids that is ejected in each opening action.
In the performance of total dumping, the drum is opened wide and the entire content of the drum is ejected by letting control fluid out of both divisions of the closing chamber by means of the valves installed in the discharge passages.
It has been found disadvantageous in this centrifugal separator design that the piston valve does not open the gap at the periphery of the drum rapidly enough and far enough during complete dumping, since the two separately operated valves for the release of the control fluid can not be opened uniformly. A rapid and wide opening of the discharge gap in total dumping is necessary, however, in order that first the solids in the solids chamber will be ejected, and only then will the remaining product fluid be ejected.
In the event of a lagging drum opening, the danger exists that the product fluid will first be ejected through the solids ring in the solids chamber which breaks up during the emptying action, and then residues of solids will remain in the drum and might result in a dangerous imbalance of the drum. To eliminate this danger, the opening action has to be performed in a fraction of a second, and this is not possible with the two separately operated valves, since the valves are situated at different distances from the center and also open differently under the action of centrifugal force.
Furthermore, it has been found disadvantageous that, in the case of small opening widths and slow closing of the piston valve, the faces and gaskets on the piston valve and drum cover which seal the discharge gap are subject to severe wear due to the longer time which the solid matter or product liquid takes to flow through it.
In the case of partial dumping, there is the disadvantage in the known design that in each case only uniform opening times of the piston valve can be achieved according to which of the closing chambers is still filled in each case, and thus there is no way of controlling the concentration that is produced in the ejected solids.